1. Field of the Invention:
The invention relates to polymers for the impact resistance modification of aromatic polycarbonates and thermoplastic molding compounds containing an aromatic polycarbonate and the impact resistance modifier.
2. Discussion of the Background:
Of the materials used to manufacture moulded plastic articles, thermoplastics are particularly important, especially thermoplastics that clearly exhibit heat resistance above 100.degree. C. Thermoplastics having a relatively high heat resistance include polycarbonates, which are usually polycondensates based on bisphenol A. The polycarbonate based on tetramethyl bisphenol A, which in turn is a condensation product of 2,6-dimethylphenol and acetone, is characterized by a glass transition temperature that is approximately 50.degree. C. higher than the "normal" bisphenol A polycarbonate. Its Vicat B softening temperature is 198.degree. C. and yet it is still thermoplastically processible.
However, for many of the desirable applications of plastics, e.g., in the construction of automobiles and vehicles, the polycarbonate properties must be improved. In the case of plastics that are becoming more important as a modern construction material, the strength upon impact stress is an important property. One measure for the strength of a plastic is the value of the notched impact strength that can be experimentally determined according to DIN 53 453 and which gives information about how a polymeric material absorbs and transforms sudden mechanical stresses.
A problem which has existed for a long time in engineering, is to transform relatively brittle plastics into industrially usable products with improved impact strength. One method of improving the strength of thermoplastics, even polycarbonates, is to improve their rubber elasticity, as reported by D. Neuray and K.H. Ott in Applied Macromol. Chem., Vol. 98, pp. 213-224 (1981). It is also stressed in this reference that rubber segments must be anchored in or "coupled" to the thermoplastic matrix, since otherwise no improvement in strength is achieved even when the elastomer content is increased. The anchoring of elastomers is achieved, for example, by means of grafting the rubbers onto polymers containing monomers that by themselves can be polymerized to thermoplastic materials.
The improvement of the impact strength of the polycarbonate by means of the addition of graft elastomers is often described. Thus DE-OS 26 53 143 or the DE-OS 26 53 145 recommend graft polymers of styrene and/or methyl methacrylate and/or (meth)acrylonitrile on diene or EPDM rubber for the preparation of thermoplastic molding compounds with polycarbonate. DE-OS 32 45 292 describes a thermoplastic molding compound comprising polycarbonate and a copolymer that comprises a polymer with a multilayered construction, whereby the core is acrylic rubber and over which a graft sheath comprising in particular (.alpha.-methyl)styrene/acrylonitrile/methyl methacrylate is applied. The polymer compound also contains an additional, separately prepared hard component, prepared from the monomers styrene, .alpha.-methyl styrene, acrylonitrile, methyl methacrylate, maleic acid anhydride and/or acrylic acid.
The European patent application 0 036 127 describes polycarbonates with improved impact strength in the form of a mixture of a polycarbonate resin and an acrylic rubber exhibiting interpolymer bonding, which contains diallyl maleate as the grafting monomer and methyl methacrylate as the monomer of the second polymer phase.
A polymer blend containing polycarbonate and an EPDM-g-methyl methacrylate/N-phenylmaleimide graft polymer is described in the European patent application 0 144 213.
Also from the European patent application 0 260 558 thermoplastic compounds containing polycarbonates and thermoplastic graft polymers based on silicone rubber with good toughness have become known, whereby the silicone rubbers for improved grafting onto resinforming monomers are provided with an intermediate sheath made of cross-linked acrylic rubber.
The DE-OS 31 18 526 describes thermoplastic molding compounds containing polyalkylene terephthalate, polycarbonate, and a graft polymer, whereby the graft polymer can also be an acrylic rubber core, constructed with aromatic esters such as benzylacrylate and phenylethylacrylate.
Compatible polymer mixtures containing polycarbonate and thermoplastically deformable methyl methacrylate copolymers are known. According to the German patent application P 36 32 946.0, the compatibility of the polymethyl methacrylate is induced with N-cyclocompound substituted (meth)acrylamides or, according to the German patent application 37 09 562.5, with N-cyclohexyl- or N-phenyl-substituted maleimides or, according to the German application P37 19 239.6, with cycloaliphatic or aromatic (meth)acrylic esters, as the comonomers.
In spite of the numerous attempts to improve the impact strength of polycarbonates, new and superior impact strength modified polycarbonates remain an important scientific and industrial objective.